U.S. Pat. No. Re. 24,906 (Ulrich) concerns a pressure-sensitive adhesive tape, the adhesive of which consists essentially of a copolymer of 88-97 parts of alkyl acrylate and correspondingly 12-3 parts of copolymerizable monomer such as acrylic acid. That acrylate copolymer provides excellent adhesion and holding power and experiences no observable deterioration even after years of storage.
To improve certain properties, the acrylate copolymer adhesive has been crosslinked. U.S. Pat. No. 2,973,286 (Ulrich) teaches that solvent resistance is improved by crosslinking by adding an organic peroxide prior to coating and applying somewhat greater heat than would be necessary merely to dry the coating. U.S. Pat. No. 2,925,174 (Stow) teaches crosslinking the acrylate copolymer by reaction with a polyfunctional compound such as a polyamine, a polyol or a polyepoxide. Because crosslinking substantially reduces tackiness, care may be taken to minimize the crosslinking until after the tape has been applied to its intended use, and then heating completes the crosslinking. The pressure-sensitive adhesive acrylate copolymer of the tape of U.S. Pat. No. 4,286,047 (Bennett et al.) contains oxirane groups which can be activated by ultraviolet radiation to become so highly crosslinked that it becomes substantially tack-free. This permits delicate electronic components to be removed easily from the tape, even though they were difficultly removable before it was crosslinked. U.S. Pat. No. 3,284,423 (Knapp) and U.S. Pat. No. 3,740,366 (Sanderson) also concern crosslinkable pressure-sensitive adhesive acrylate copolymers.
Although it is recognized that crosslinking can improve the adhesive properties of a pressure-sensitive adhesive, it has been necessary to use other types of adhesives such as liquids in many applications where the convenience of a pressure-sensitive adhesive tape would have been highly desirable.